Replies to 'Cheated On'

As I said before, it is rather dificult for me to get out and safely drive; due to a medical condition.  I think he takes advantage of this. He knows every 2 weeks I am not comfortable driving long distances, if I have to I take side streets and avoid the highway.  Should I continue to trust my instinct? I believe I should.  As for the computer at his work, he had told me that only his coworkers e-mail him and me. Then he says he got an e-mail from his brother. That's no big deal; what is is the fact that he has lied about it. HIs brother doesn't work for his company. If he has lied about that, I'm most certain he has lied about other isssues. For instance, One day we were talking about having sex in his office and I said I would want it cleaned before we do. Since other people (bosses) have access to the office, you never know what they are doing behind closed doors. He didn't say anything, but looked down with a guoilty look on his face. That told me, he has entertained other people in his office. What would you think if you had this conversation with your husband and he reacted the same way? Asking him won't get me anywhere for he will deny it and say I don't trust him.  Which at this point is true.  I can recall another time when I was talking on the phone with a friend. We were discussing how her boyfriend had chated on her. When I got off he said to me "you know nothings going on, right?"   No man says that or says "prove that I am not" without actually being guilty of the act. What do oyu think?  Should I come right out and tel him I don't need proof to tell me of your guilt for you have done it yourself? or should I loet it lie and hope that I find substantial evidence? Still confused on how to handle this, but not blind nor dumb. How do I get the trtith out of him?